The conventional automatic sprinkler head is connected to a water line and includes a body or frame that has an outlet orifice which is normally closed by a cap, and the cap is held in the closed position by a lever assembly which includes a low melting point fusible element. When the ambient temperature is increased to a predetermined level, the element will melt, releasing the lever assembly to open the orifice and discharge the water.
In residential dwellings and commerical buildings, it is often desired to utilize a sprinkler head that is located above the ceiling so that the operative parts are not exposed to view. In some cases, the sprinkler head is mounted within a recess in the ceiling, and while the sprinkler head does not depend from the ceiling, the operative parts are not completely concealed.
In other instances the sprinkler head is concealed within the ceiling by a decorative plate which is mounted flush against the ceiling so that none of the operative parts are visible.
In some concealed sprinkler head installations, such as disclosed in U.S. Pat. Nos. 3,633,676 and 3,714,989, the decorative plate is attached to the sprinkler head by a fusible material, and when the fusible material melts, the decorative plate is released to expose the fusible element of the lever assembly. Sprinkler heads of this variety have a disadvantage in that two separate fusible release mechanisms are required, one to release the decorative plate to expose the fusible element of the lever assembly, and the second to release the lever assembly to open the orifice.
With either the recessed or concealed types of sprinkler head, the rate of heat transfer to the fusible element is reduced so that recessed and concealed types of sprinkler heads generally have a slower response rate than the exposed type of sprinkler head.